Although there is now solid evidence to support the efficacy of colorectal cancer screening, few health care systems have developed comprehensive screening programs. This report describes the scientific rationale, development and implementation strategies, and preliminary results of the Colon Cancer Prevention Program (CoCaP) of the Northern California Region of the Kaiser Permanente Medical Care Program. CoCaP is a sigmoidoscopy-based screening program that aims to provide screening to all average-risk program members once every 10 years beginning at age 50. During the first 2 years of the program, more than 100,000 sigmoidoscopies were performed in age-eligible members (age 50 years and above). Seventy-five percent of these were screening examinations. Participating endoscopists include gastroenterologists, generalist physicians, and a growing number of non-physicians, primarily nurses, nurse-practitioners or physicians' assistants. Data on depth of insertion and polyp yield suggest that non-physicians quickly become as proficient as physician endoscopists. The long-term goals of the CoCaP program are to reduce the incidence of and mortality from colorectal cancer. Collection and analysis of data from the screening examinations and follow-up colonoscopies will enable CoCaP to refine its screening algorithm and to quantify program effectiveness.